1. Field of the Invention
This invention relates to a liquid crystal display and to a method of fabricating a hologram diffuser for a liquid crystal display that is adapted to widen a visual angle of the liquid crystal display.
2. Description of the Related Art
Liquid crystal displays (LCDs) are gaining wider application due to their characteristics of light weight, thin thickness, and low power consumption. Accordingly, the LCDs have been used in office automation equipment, in audio/video equipment, etc. An LCD controls a transmitted amount of a light beam in accordance with image signals applied to a number of control switches arranged in a matrix to display a desired picture on a screen. However, this type of LCD has a drawback arising from the narrow visual angle of the liquid crystal. The display quality considerably deteriorates when being viewed beyond the visual angle range. The visual angle of the LCD is described with reference to FIG. 1 below.
Referring to FIG. 1, a conventional LCD includes a back light unit 10 for generating and uniformly supplying a light beam. A lower polarizer 12 arranged above the back light unit 10 changes a polarization characteristic of the light beam. A lower substrate 14 is arranged above the lower polarizer 12 and provided with switching devices (not shown) in a matrix for controlling the transmitted amount of the light beam. A liquid crystal layer 16 is formed on the lower substrate 14, and a color filter layer 18 formed on the liquid crystal layer 16. An upper substrate 20 is arranged on the color filter layer 18, and an upper polarizer 22, arranged above the upper substrate 20, converts a polarization characteristic of the light beam.
In FIG. 1, the back light unit 10 has a light source for generating a light beam, a light-guide plate for uniformly guiding the light beam generated from the light source into a liquid crystal panel, and a reflective plate positioned under the light-guide plate to reflect a light beam going to the lower surface or the side surface of the light-guide plate toward the liquid crystal panel. This configuration allows the uniform progression of the light beam from the back light unit 10 into the liquid crystal panel. The light beam is polarized by means of the lower polarizer 12. The polarized light beam passes through a liquid crystal layer 16 controlled by means of the switching devices (not shown), where its polarization direction rotates.
In FIG. 1, the light beam having its polarization direction rotated by the liquid crystal layer 16 passes through the color filter layer 18 to yield a color wavelength corresponding to each color filter. The light beam realized into the desired color by the color filter layer 18 progresses, via the upper substrate 20, into the upper polarizer 22. The upper polarizer 22 and the lower polarizer 12 are crossed to be perpendicular to each other. Thus, the upper polarizer 22 transmits only light having its polarization direction rotated by means of the liquid crystal.
As described above, a basic principle of the TN-mode (twisted nematic mode) LCD is to utilize a polarized light beam (polarized by means of the polarizers) which passes through the liquid crystal so that its polarization direction rotates. Thus, the distance the light beam progresses through the liquid crystal layer 16 becomes very significant. Generally, in the case of a liquid crystal provided between polarizers crossed perpendicular to each other, the thickness of the liquid crystal used to change the polarization direction of a light beam is given by the following equation:(Δn)Z=λ/2  (1)wherein Δn represents the refractive index difference between the perpendicular direction and the parallel direction of the incident light (which appears as a complex refraction characteristic of the liquid crystal); Z represents the thickness of the liquid crystal; and λ is the wavelength of light. In this case, an effect identical to equation (1) is obtained when the direction of the light is perpendicular to the liquid crystal panel, and the result is a reliable light shut-off. However, an accurate light shut-off cannot be obtained by the upper perpendicular polarizer because the light path increases when the light runs with an inclination, thereby generating a change in the polarization direction of the light. In order to overcome this problem, the linearity of a light beam must be increased.
If the linearity of a light beam is increased, then the visual angle of the LCD becomes limited. Widening the visual angle requires a diffusion layer capable of again scattering the light beam passing through the liquid crystal layer 16. In the conventional method, the diffusion layer is arranged between the upper substrate and the upper polarizer. For example, if the diffusion layer is used as a lens array, a lenticular lens sheet and a cholesteric liquid crystal (CLC) can be used.
When a diffusion layer is employed to widen the above described visual angle of the LCD, the color purity and picture quality of the LCD deteriorates due to the blending of the light beams emitting from each of the R (red), G (green) and B (blue) pixels. As a result, it becomes necessary to provide a novel scheme for solving the above problems.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.